The present invention relates to an odor measuring apparatus which measures odor components contained in a sample gas, and more particularly, it relates to an odor measuring apparatus for indicating a degree of odor in an index value, such as an odor index and an odor intensity. An odor measuring apparatus according to the present invention can be used in a wide range of fields, such as quality inspection for food or perfume, quantitative detection of malodor pollution, fire alarm by a scorched or burnt odor, and criminal investigations including tracking, identification, and authentication of a person, or drug test.
Conventionally, in order to find an odor index or odor intensity that is so-called organoleptic or sensitive intensity value, a sensory test in which a human""s olfaction or sense of smell is actually used. The method of the test as described above is defined in, for example, xe2x80x9cMETHOD OF CALCULATING AN ODOR INDEXxe2x80x9d in Notification No. 7 (1996) of the Environment Agency in Japan. Also, regarding substances, such as twenty-two kinds of substances (for example, hydrogen sulfide, formaldehyde) causing malodor which have been already defined in a xe2x80x9cAKUSHU BOSHI HO (Malodor Prevention Law in Japan)xe2x80x9d, in which correlation between a concentration of a substance and an odor index or odor intensity is known, the concentration of the substance is measured by an instrumental analysis using an analyzer, such as a gas chromatography, and the concentration is converted into the odor index or the odor intensity.
Although the sensory test described above has been used widely heretofore, since a person""s olfaction is utilized, it has to be understood that a sense of smell changes in accordance with an individual difference and a daily condition of a person who smells an odor (hereinafter referred to as a panel). Therefore, in order to obtain an objective result accurately, it is necessary to use a predetermined number of panels or more, and an environment of a test site or the like must be considered well. Thus, it requires a large amount of labor and time therefor.
On the other hand, in the odor analysis utilizing the analyzer, the odor index or odor intensity can be calculated regarding a limited, single substance as described above. However, in reality, most of odors exhausted by industrial activities are compound odors in which a plurality of substances is mixed, and the conventional odor analysis utilizing the analyzer has a disadvantage that the odor index of the compound odor can not be computed.
The present invention has been made in view of the foregoing, and an object of the invention is to provide an odor measuring apparatus which can easily and accurately find an index value of odor that was obtained by the organoleptic test by a panel conventionally.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the above object, the present invention provides an odor measuring apparatus, which is formed of a plurality of detecting means having different characteristics to detect odor components in a sample gas; odor fractionating means for determining which one of odor categories an odor in the sample gas belongs to based on a plurality of detection outputs obtained from the detecting means; and computing means for calculating an index value regarding the odor based on the detection outputs obtained from the detecting means by using a regression line determined in advance for each of the odor categories.
As the detecting means, there can be effectively used so-called odor sensors, which electrically or optically measures physical changes of the sensors occurring when odor components contained in air or the supplied sample gas adhere to sensitive films of the sensors. As the odor sensors, there are sensors using oxide semiconductors, or sensors using conductive high polymers.
In particular, the odor measuring apparatus of the invention includes a plurality of different kinds of odor sensors which are different in structures, or materials for sensitive films, and by exposing the odor sensors in a sample gas, a plurality of detection outputs is obtained. The odor fractionation means uses the plurality of detection outputs, and fractionates the odor of the sample gas into one of the odor categories or ranges. Here, the odor categories mean classification of sensuous odors, such as a burnt odor and a rotten odor, irrespective of the materials contained in the sample gas. In order to fractionate these kinds of the odors, for example, there can be used various kinds of methods, such as a method of determining a similarity of combination patterns of the plurality of detection outputs, a method of using various techniques of multivariate analyses, that is, a cluster analysis and a principal component analysis, and a method of using a neural network.
Then, the computing means calculates an index value, such as an odor index or odor intensity, by a regression analysis method based on the plurality of the detection outputs. At this time, information regarding the odor categories, i.e. qualities of the odors, obtained before is utilized. According to the experiments by the inventors of the present invention, as long as the appropriate odor categories are set, even if contents or substances are different, the same regression line can be utilized for each odor category in order to compute the index value, such as the odor index. Namely, a regression coefficient can be determined in advance for each category of the odor, and at the time of measuring the odor, the index value is computed from the regression coefficient and the plurality of the detection outputs.